You don't know what you are taking about.
First of all, don't lump D3 in with D2 or D1. D3 was SO bad that they outright scrapped the second xpac. D3 failed.
Second of all, Blizzard has driven off the majority of ARPG fans. Its YOU that is on your own little island of what makes an ARPG good. Diablo is a cornerstone franchise and should have a massive massive playerbase.
Second of all, don't compare the multiplayer version of D2 in 2000 with what is required from a multiplayer version in 2020. Yup, D2 had offline play. But, for its time, D2 was the BLEEDING EDGE of multiplayer online ARPG. That gave it a massive value-add. There is no value add in D3. And there is no value add in mostly singleplayer D4.
What exactly is the selling point in your version of D4? Complete this sentence: You need to put aside all other video games and pick up D4 because ____________
There is no answer to that with singleplayer D4. The ARPG market is flooded with singleplayer ARPG. They are all cannibalizing each other's playerbases. That is a recipe for failure. You've got to step up and do something different. And Diablo can do that by focusing on multiplayer and community.
Diablo should have a massive following.
This reminds me of talking to people about WoW. WoW once had like 12-14 million players. Blizzard drove them ALL off in an insane devotion to antisocial play. Then we get down to like 2-3 million today, and when you suggest they should return to social play, they say "don't drive off the playerbase, you are on your own little island with your opinions". I mean holy crap. They've already driven almost everyone off.
Honestly, i think the Blizz devs would rather let WoW die before actually fixing the game and rebuilding the social scene. And I think they are dong it to Diablo as well. Its SOOOOOO stupid. Its like watching Yahoo! mismanage itself in its final years.